1. Field of the Invention
The present invention relates generally to an immersion type motor driven complex pump apparatus including two independent pumps which may be driven by a single motor, wherein the motor is arranged above the surface level of a liquid to be pumped, while the pumps are immersed in a bath containing the liquid. More particularly, the present invention relates to a motor driven complex pump apparatus preferably employable as a coolant pump for pumping a cooling solution for a machine tool, wherein the complex pump apparatus comprises a centrifugal pump and a half-shrouded pump including a volute chamber.
2. Description of the Prior Art
For example, a single stage type centrifugal pump as prescribed by the Japan Electric Machinery Association in standard rule JEM 1242 (1970) entitled "Coolant Pump" is known as a pump employable in the field of machine tools. In addition, a multistage pump as disclosed in an official gazette of Japanese Patent Application Laid-open (Kokai) No. 62-189399 is known as a multistage immersion type pump. Further, complex pumps as disclosed in Japanese Patent Application Laid-open No. 63-32195 and Japanese Utility Model Application Laid-open No. 1-97032 are known as general complex pumps. Usually, as a coolant pump for machine tools, two or more motor driven complex pumps are used for each machine tool in such a manner that a pressure type motor driven pump is employed for the purpose of lubricating and cooling a cutting/grinding surface of a workpiece and blowing chips or ground particles generated by the cutting/grinding operation, while a flow rate type motor driven pump is employed for the purpose of washing chips or ground particles away from a bed of a machine tool.
According to the prior art described above, there is a necessity for reserving the space required for installing two or more motor driven pumps for each machine tool. To satisfactorily meet the foregoing necessity, a problem arises in that two or more wiring systems should be arranged for driving electric motors for the pumps. In the case where the pressure type motor driven pump and the flow rate type motor driven pump are operated under the same conditions a similar problem arises when two sets of the same motor driven pumps are used. Under some circumstances, two discharge tube systems are arranged corresponding to a single pump having double the flow rate since the pump has the same combined pump properties of the aforementioned pumps. In this case, when one of the two discharge tube systems is fully closed or partially closed, the flow rate of a liquid flowing through the other discharge tube systems varies. To avoid the foregoing malfunction, two sets of identical motor driven pumps should be used.